Listing 3 Adding the extension 555 to fire your text-to-speech AGI script in Asterisk. You are merely telling Asterisk to answer the extension, run the AGI script, and play back the sound file you have created. The final step is to hang up after the playback.

[nagios]
exten => 555,1,Answer
exten => 555,2,AGI(nagios.php)
exten => 555,3,Playback(nagiosalert)
exten => 555,4,Hangup